This invention relates to simulation systems for testing an imaging infrared seeker, and in particular to such system for converting scene composition data stored in a digital computer into an infrared image suitable for projection to the seeker.
One type of known missile guidance system employs a seeker that extracts from the infrared images in its field of view the information upon which the missile guidance system bases its in-flight flight path corrections. The testing of such imaging infrared seekers requires an imaging infrared simulator which is capable of presenting realistic, detailed infrared images, i.e., scenes, to the field of view of the seeker. The infrared scenes presented to the seeker's field of view must simulate both the infrared characteristics of a potential missile target and the different background scenes in which the target is likely to be found.
Closed loop testing of the seeker mounted on a flight table imposes a random access requirement upon the updating of certain infrared imaging scenes. The random access requirement can be supplied by interpolation techniques of scene composition supplied by infrared imagery data stored in digital computers such that the data can be provided in streams to update the scene. To exploit this capability, however, a device must be able to convert the electronic signal of the digital computer into an infrared image suitable for projecting into the field of view of the missile seeker.
Conventional systems that have been developed to fill this need suffer from a serious difficulty known as "shading," which is a time-dependent variation in the radiation projected as the infrared scene. Shading results from serially "writing" the infrared scene data onto devices whose storage time constant approximates the scene update period. Shading affects the contrast signatures of the images of the target and the background, and a significant amount of shading causes breakdown of the simulation.
One approach involves the use of a Bly cell, such as the one described in U.S. Pat. No. 4,178,514, to convert a visible light input into an infrared light output. However, a Bly cell exhibits a relatively short time constant and therefore requires an "all-at-once" input rather than a serially written input if shading is to be avoided.